1. Field of the Invention
The present invention relates to an ink-jet head that ejects ink onto a recording medium to conduct recordings, and also to a method for manufacturing the ink-jet head.
2. Description of Related Art
In some ink-jet heads used in ink-jet recording apparatuses such as ink-jet printers, three linear pressure chambers are arranged on a surface of a passage unit having ink passage as formed therein such that the three linear pressure chambers are adjacent to each other with respect to a perpendicular direction to their linear direction, and, in addition, a piezoelectric actuator spanning the three pressure chambers is arranged on the surface of the passage unit on which the pressure chambers are formed (see U.S. Pat. No. 5,402,159). The piezoelectric actuator has a plurality of piezoelectric sheets constituting a piezoelectric element. A common electrode shared by all the pressure chambers and three individual electrodes each corresponding to each pressure chamber are disposed at different levels between the plurality of piezoelectric sheets. The common electrode is always kept at the ground potential, while the individual electrodes are under independent potential controls. The piezoelectric sheets are polarized in their thickness direction. Portions of the piezoelectric sheets sandwiched between the individual electrodes and the common electrode act as active portions. When the individual electrodes are set at a different potential from that of the common electrode, the active portions of the piezoelectric sheets expand or contract in their thickness direction. Thereby, the pressure chambers located under the active portions change in volume, and pressure is applied to ink reserved in the pressure chambers, so that the ink is ejected toward a recording medium from nozzles communicating with the pressure chambers in the passage unit.
Both the common electrode and the individual electrodes are formed by arranging conductive pastes in a predetermined pattern on the piezoelectric sheets or on green sheets to develop into the piezoelectric sheets, and then firing to sinter the pastes.
Such a construction may involve a problem that, among nozzles communicating with the respective pressure chambers in a pressure chamber group consisting of a plurality of adjacently-arranged pressure chambers, the nozzles that communicate with pressure chambers located outermost with respect to an arrangement direction of the plurality of pressure chambers and the nozzles that communicate with the other pressure chambers located inside exhibit different ink ejection characteristics from each other. Since a variation in ink ejection characteristics leads to deterioration in quality of images to be printed, suppression of the variation in ink ejection characteristics is of great importance in an ink-jet head.